Class Implement No More

<?php

try {
    $x = initSomething();
    doSomething();        // may throw an exception
}

// no catch: exception keep their way

// finally is always executed
// with or without exception being caught
finally{
    $x->shutdown();
}

?>

Inheritance forces children classes to have only methods that are compatible with the parent’s methods.

The only exception is the constructor, which may have a totally different signature from generation to generation.

Interfaces apply the same constraints: their methods signature must be compatible with the host class. In this case, it also applies to the constructor.

So, in the case a parent class implements an interface with a constructor, and this class has a child class, the child may look compatible with the interface, and yet, be invalid at the constructor level.

Another good reason to avoid placing constructors in interfaces.

See Also

• Object Interfaces (PHP manual)

• No need for catch with try [Try me]

PHP Features

• catch

• try-catch

Last updated: 14 July 2026